The Unit on Neuroimaging has focused on studies of a simple form of learning and memory--eyeblink conditioning--in the past year. Using positron emission tomography (PET), we were able to demonstrate changes in regional cerebral blood flow which occurred during this form of associative learning in a group of young normal volunteers. Changes in areas such as the cerebellum, prefrontal cortex, and neostriatum provide support for the roles of these structures in associative learning as proposed by animal models. The increased and decreased regional cerebral blood flow in a number of structures throughout the brain too, showed that in humans, even simple classical conditioning involves distributed changes in multiple neural systems. Of particular interest was the finding that regional cerebral blood flow was increased in primary auditory cortex with learning. This was the first example, using a neuroimaging technique, of a learning-related change in primary sensory cortex in humans. Simple forms of learning such as classical conditioning may well constitute integral components of higher cognition. By using the paradigm, we hope to learn more about how normal memory works, and how it may become disrupted in normal aging and in Alzheimer's disease.